维护者确认：#2993 feat(desktop): support nested list indentation in composer

PR [#2993](https://github.com/makecindy/cindy/pull/2993) 触发了维护者确认门。

**触发原因：**
- product：feat 类型 + 命中 UI 路径（ChatInput.tsx 等）
- arch：huge-diff（811 行 ≥ 800）

新增 composer 嵌套列表缩进功能，属于新产品特性。

**确认方式：**
- 直接在 PR 上 Approve → 放行
- Request Changes → 等作者修改后重新 Approve 即放行

---
关联 PR:#2993(作者 @guwenxi-gugu);本 issue 由 review-pr 流程自动创建,用于先讨论该 PR 涉及的产品 / UI 变更,维护者确认后 PR 会恢复推进。

This is a maintainer-confirmation issue for PR #2993, not an implementation task. Review PR #2993, starting with the mentioned ChatInput.tsx/UI path, and decide whether the nested-list indentation feature should be approved or sent back for changes. Done means the PR is approved or has requested changes.

Written by the indexing model from the issue text.